At least seven inmates have been killed during a riot at a Brazilian jail, the sixth in Sao Paulo state this week.

They died from smoke inhalation after prisoners set fire to mattresses in the Jundai jail, in the state of Sao Paulo. The uprising started on Wednesday as inmates protested against the transfer of some of prisoners to another jail.

The inmates at the Jundai jail, about 30km (19 miles) west of Sao Paulo, took several guards and police officers hostage, but later freed most of them.

The Brazilian authorities said prisoners still controlled part of the jail, and negotiations were under way to try end the standoff.

The Jundai prison was designed to hold 120 inmates, but 470 are detained there.

In the past, rioting has been blamed on poor living conditions, but also on organised crime gangs that enjoy power and influence in the penitentiary system.